[dev.regabi] cmd/compile: cleanup export code further

This CL rips off a number of toolstash bandages:

- Fixes position information for string concatenation.

- Adds position information for struct literal fields.

- Removes unnecessary exprsOrNil calls or replaces them with plain
  expr calls when possible.

- Reorders conversion expressions to put type first, which matches
  source order and also the order the importer needs for calling the
  ConvExpr constructor.

Change-Id: I44cdc6035540d9ecefd9c1bcd92b8711d6ed813c
Reviewed-on: https://go-review.googlesource.com/c/go/+/279957
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/typecheck/iexport.go

@@ -858,8 +858,6 @@ func intSize(typ *types.Type) (signed bool, maxBytes uint) {
 // according to the maximum number of bytes needed to encode a value
 // of type typ. As a special case, 8-bit types are always encoded as a
 // single byte.
-//
-// TODO(mdempsky): Is this level of complexity really worthwhile?
 func (w *exportWriter) mpint(x constant.Value, typ *types.Type) {
 	signed, maxBytes := intSize(typ)
 
@@ -1154,7 +1152,6 @@ func (w *exportWriter) stmt(n ir.Node) {
 		w.op(n.Op())
 		w.pos(n.Pos())
 		w.stmtList(n.Init())
-		w.exprsOrNil(nil, nil) // TODO(rsc): Delete (and fix importer).
 		w.caseList(n.Cases, false)
 
 	case ir.OSWITCH:
@@ -1298,7 +1295,7 @@ func (w *exportWriter) expr(n ir.Node) {
 			s = n.Tag.Sym()
 		}
 		w.localIdent(s, 0) // declared pseudo-variable, if any
-		w.exprsOrNil(n.X, nil)
+		w.expr(n.X)
 
 	// case OTARRAY, OTMAP, OTCHAN, OTSTRUCT, OTINTER, OTFUNC:
 	// 	should have been resolved by typechecking - handled by default case
@@ -1333,7 +1330,8 @@ func (w *exportWriter) expr(n ir.Node) {
 		n := n.(*ir.KeyExpr)
 		w.op(ir.OKEY)
 		w.pos(n.Pos())
-		w.exprsOrNil(n.Key, n.Value)
+		w.expr(n.Key)
+		w.expr(n.Value)
 
 	// case OSTRUCTKEY:
 	//	unreachable - handled in case OSTRUCTLIT by elemList
@@ -1397,8 +1395,8 @@ func (w *exportWriter) expr(n ir.Node) {
 		n := n.(*ir.ConvExpr)
 		w.op(ir.OCONV)
 		w.pos(n.Pos())
-		w.expr(n.X)
 		w.typ(n.Type())
+		w.expr(n.X)
 
 	case ir.OREAL, ir.OIMAG, ir.OCAP, ir.OCLOSE, ir.OLEN, ir.ONEW, ir.OPANIC:
 		n := n.(*ir.UnaryExpr)
@@ -1529,6 +1527,7 @@ func (w *exportWriter) fieldList(list ir.Nodes) {
 	w.uint64(uint64(len(list)))
 	for _, n := range list {
 		n := n.(*ir.StructKeyExpr)
+		w.pos(n.Pos())
 		w.selector(n.Field)
 		w.expr(n.Value)
 	}

src/cmd/compile/internal/typecheck/iimport.go

@@ -851,8 +851,7 @@ func (r *importReader) node() ir.Node {
 		if s := r.ident(); s != nil {
 			tag = ir.NewIdent(pos, s)
 		}
-		expr, _ := r.exprsOrNil()
+		return ir.NewTypeSwitchGuard(pos, tag, r.expr())
-		return ir.NewTypeSwitchGuard(pos, tag, expr)
 
 	// case OTARRAY, OTMAP, OTCHAN, OTSTRUCT, OTINTER, OTFUNC:
 	//      unreachable - should have been resolved by typechecking
@@ -864,19 +863,16 @@ func (r *importReader) node() ir.Node {
 	//	unreachable - mapped to case OADDR below by exporter
 
 	case ir.OSTRUCTLIT:
-		pos := r.pos()
+		return ir.NewCompLitExpr(r.pos(), ir.OCOMPLIT, ir.TypeNode(r.typ()), r.fieldList())
-		return ir.NewCompLitExpr(pos, ir.OCOMPLIT, ir.TypeNode(r.typ()).(ir.Ntype), r.elemList(pos))
 
 	// case OARRAYLIT, OSLICELIT, OMAPLIT:
 	// 	unreachable - mapped to case OCOMPLIT below by exporter
 
 	case ir.OCOMPLIT:
-		return ir.NewCompLitExpr(r.pos(), ir.OCOMPLIT, ir.TypeNode(r.typ()).(ir.Ntype), r.exprList())
+		return ir.NewCompLitExpr(r.pos(), ir.OCOMPLIT, ir.TypeNode(r.typ()), r.exprList())
 
 	case ir.OKEY:
-		pos := r.pos()
+		return ir.NewKeyExpr(r.pos(), r.expr(), r.expr())
-		key, value := r.exprsOrNil()
-		return ir.NewKeyExpr(pos, key, value)
 
 	// case OSTRUCTKEY:
 	//	unreachable - handled in case OSTRUCTLIT by elemList
@@ -919,9 +915,7 @@ func (r *importReader) node() ir.Node {
 	// 	unreachable - mapped to OCONV case below by exporter
 
 	case ir.OCONV:
-		pos := r.pos()
+		return ir.NewConvExpr(r.pos(), ir.OCONV, r.typ(), r.expr())
-		x := r.expr()
-		return ir.NewConvExpr(pos, ir.OCONV, r.typ(), x)
 
 	case ir.OCOPY, ir.OCOMPLEX, ir.OREAL, ir.OIMAG, ir.OAPPEND, ir.OCAP, ir.OCLOSE, ir.ODELETE, ir.OLEN, ir.OMAKE, ir.ONEW, ir.OPANIC, ir.ORECOVER, ir.OPRINT, ir.OPRINTN:
 		n := builtinCall(r.pos(), op)
@@ -973,7 +967,6 @@ func (r *importReader) node() ir.Node {
 		pos := r.pos()
 		list := r.exprList()
 		x := list[0]
-		x.SetPos(pos) // TODO(mdempsky): Remove toolstash bandage.
 		for _, y := range list[1:] {
 			x = ir.NewBinaryExpr(pos, ir.OADD, x, y)
 		}
@@ -1041,7 +1034,6 @@ func (r *importReader) node() ir.Node {
 	case ir.OSELECT:
 		pos := r.pos()
 		init := r.stmtList()
-		r.exprsOrNil() // TODO(rsc): Delete (and fix exporter). These are always nil.
 		n := ir.NewSelectStmt(pos, r.caseList(nil))
 		n.PtrInit().Set(init)
 		return n
@@ -1088,12 +1080,10 @@ func (r *importReader) op() ir.Op {
 	return ir.Op(r.uint64())
 }
 
-func (r *importReader) elemList(pos src.XPos) []ir.Node {
+func (r *importReader) fieldList() []ir.Node {
-	c := r.uint64()
+	list := make([]ir.Node, r.uint64())
-	list := make([]ir.Node, c)
 	for i := range list {
-		// TODO(mdempsky): Export position information for OSTRUCTKEY nodes.
+		list[i] = ir.NewStructKeyExpr(r.pos(), r.ident(), r.expr())
-		list[i] = ir.NewStructKeyExpr(pos, r.ident(), r.expr())
 	}
 	return list
 }